Since it would appear that the little tidbits of V4 are scattered all across the forum, I'm just collecting a few. I've likely missed quite a few, so feel free to correct me.
Uruk Dominion
Reptarri Upgraded Version
Paynal/Kukul
Raptor Riders:
Gaulic Nations
Gaulic Swordsmen:
Axe-Throwers
Druids
Romuli
Praetorian Purgationes:
Faustian Reich
Will acquire a new Serpentine gunner model
which will involve a new rapier-style sword as a secondary
Grand Duchy of Dracule
New Dismounted Blood Knights Light Version:
Dark Version:
Mounted Blood Knights
Barka Sultanate
Immortal Model (new)
alas, those were all that I could find in my first scouring of the forums, but I'm sure there's more to it than that!